This invention relates to a power entry module for supplying electrical power from an external source, usually A.C. line power. The power entry module is of the type which includes a plug receptacle for connecting a line power cord or cable which is detachable from the entry module. The power entry module also includes a fuse between the A.C. line power source and the remainder of the apparatus to which it is connected to prevent damage to the apparatus if excessive amounts of current are drawn and further, includes voltage selecting mean for switching the module for drawing voltage at a particular level and converting it to a voltage usable by the electrical instrument or apparatus with which it is associated.
U.S. Pat. No. 3,728,586 to Inhelder et al. teaches an A.C. power module with a power receptacle contained in one compartment of the module and a fuseholder, fuse ejector and line voltage switch contained in the other compartment. A safety mechanism prevents changing the fuse or line voltage setting while the A.C. line power cord is plugged into the instrument or appliance. In the preferred embodiment the safety device is a sliding door which covers either the A.C. line power receptacle or the fuseholder, ejector and line voltage switch. When access is provided to the compartment housing the fuseholder, ejector and line voltage switch, the fuse can be changed and the current or voltage designation can be changed by access to said compartment. The fuse ejector can be triggered at that point to thereby eject the fuse prior to reconnecting the module to an outside power source.
Although generally providing the feature of a safety interrupt to prevent power from being supplied through the module when access is provided to the fuseholder portion of the module, this device is generally unreliable and complicated in that the provision of the sliding door does not ensure safety since the sliding door structure can be easily disassembled or fall apart. Moreover, the fuse ejector mechanism is generally unreliable and can easily fail making the operation of the device generally complicated in nature. Still further, the fuse ejector mechanism operation is tied in to the voltage selection function and in order for the changing of the voltage to be effected, one must necessarily first eject the fuse, reset the voltage, and reinsert the fuse regardless of whether or not the fuse in the device at the time is appropriate for the voltage at which it was set or was being reset.
An alternative approach to an A.C. power entry module is disclosed in U.S. Pat. No. 4,488,201 of Webb et al. More particularly, the Webb device includes a plate having different size fuseholders, which plate can be positioned in various different positions depending upon the fuse desired to be employed in its particular application. The plate is housed inside a portion of the module and a cover is provided over the plate. A separate compartment includes a power entry module to which a cable can be connected, and an on-off switch allows entry of power through the module. A separate portion of the module includes means for housing a voltage selector card which will convert the incoming voltage to the appropriate voltage for the device. Although generally denying access to the live power part when the cover is pulled off, if the fuse plate is also pulled out of Webb, access can be had to the live contacts of the power entry module and as such, a danger to the user exists.